This invention relates generally to toner compositions, and more specifically to encapsulated toner compositions with certain characteristics. Accordingly, in one embodiment of the present invention there are provided encapsulated toner compositions with low melting characteristics comprised of a polymeric core with pigment particles therein and a shell prepared, for example, by interfacial polymerization processes. Moreover, the encapsulated toner compositions of the present invention can contain in the core other additives inclusive of silicone oils and waxes enabling the resulting toners to be useful for incorporation into electrophotographic imaging apparatuses wherein the costly devices needed for the retaining and release of silicone oils is avoided. Specifically, therefore, the toner compositions of the present invention possess low melting properties, that is for example they melt at temperatures between 65.degree. C. and 140.degree. C.; enable superior optical densities for the images developed; and in addition, the toner compositions of the present invention especially wherein the core contains therein release fluids such as silicone oils are useful in electrophotographic imaging devices. Therefore, the toner compositions of the present invention are useful in electrophotographic, particularly xerographic imaging and printing processes inclusive of those processes wherein there is avoided the need for costly release fluid systems. The toner compositions of the present invention also enable the formation of images which have low gloss properties because of the lower pressures and lower temperature required for their fusing on paper. This lower gloss can also be attributed to the presence of a high glass transition temperature shell (greater than 60.degree. C.), which results upon fusing of the toner in uneven surfaces as the shell rheological properties are different than those of the core polymers. In addition, the present invention is directed to processes for the preparation of toner compositions, which processes in one embodiment utilizes a solvent system enabling the resulting toner to possess a density of from about 0.2 to about 0.8 gram per cubic centimeter with higher densities being achievable by selecting insitu free radical polymerization of the core components.
Encapsulated cold pressure fixable toners with improved imaging and fusing properties are disclosed in copending application U.S. Pat. No. 4,727,011, entitled Processes For Encapsulated Toner Compositions With Interfacial/Free-Radical Polymerization, the disclosure of which is totally incorporated herein by reference. These toner compositions, however, are not effective in some situations wherein there is desired carbon black based heat fusible encapsulated toners with desirable size polydispersity, and also such toners cannot usually be prepared at low cost, disadvantages alleviated with the toner compositions and processes of the present invention. For example, the toner compositions of the present invention can be prepared by a solvent based process allowing flexibility with respect to the type of materials which can be used in the core of the encapsulated toner, or a monomer based process enabling lower cost by eliminating solvent recovery. More specifically, with the process of the present invention there can be prepared carbon black based encapsulated toners by an insitu free radical polymerization process, and wherein the core of the toners can be formulated from a blend of polymers and insitu polymerized monomers thereby significantly effecting the toner fusing temperature. Thus, because of the inherent compatibility of the pigment such as carbon black with polymers, the carbon black or other pigment can be trapped in high proportion in the toner core with the process of the present invention. Another advantage achievable with the toner compositions and processes of the present invention resides in the selection of free radical polymerization of vinyl monomers and the presence of pigment particles such as carbon black, which advantage is achievable, for example, by selecting low surface area carbon black particles with neutral pHs in combination with azo initiators, which minimize the inhibition effects usually associated with higher surface area carbon blacks or, for example, by ball milling the pigment particles such as carbon black in the presence of monomer and initiator in the presence or absence of heat.
Encapsulated toner compositions, inclusive of cold pressure fixable toner compositions, are known as indicated herein. Also known are toner compositions that are heat fusible in electrophotographic imaging processes, these toner compositions generally not being encapsulated. In U.S. Pat. No. 4,533,617 there is, however, described a heat fixable developer containing a capsule structure having the surface of a core particle coated with a vinyl type polymer with a glass transition temperature of 55.degree. C. or higher, a softening point of 100.degree. to 150.degree. C., a molecular weight of 150,000 or more, and a M.sub.w /M.sub.n of 5 or more. As indicated in column 3, beginning at line 49, of this patent there is provided a heat fixing developer of a capsule structure containing in the core a binder resin with a glass transition temperature of 60.degree. C. or lower, a softening point of 50.degree. to 130.degree. C., and a colorant. Also, it is stated in column 3, beginning at line 58, that the binder resin contains an amorphous polyester or a vinyl type polymer having a crosslinked structure with a gel content of 20 percent or more as the main component. In comparison, the toner composition of the present invention, for example, does not contain a crosslinked component with a gel content of 20 percent or more as the main component of the core.
In addition, there is illustrated in U.S. Pat. No. 4,562,137 that a microcapsule rupture can be affected by pressure or other means including ultrasonic vibration, solvent vapor means, and other methods, reference column 6; and morever, in column 8, interfacial polymerization processes are illustrated. The toner composition of the present invention, while prepared by known interfacial polymerization as an encapsulation method, do not contain thereon radiation sensitive compositions such as those described in the '137 patent. In addition, of background interest there are mentioned as representative patents U.S. Pat. Nos. 4,529,681; 4,536,462 and British Patent Publication No. 2,112,538. While the subject matter of these patents is of interest, none of them teach a low melting encapsulated toner containing the components of the present invention, and in particular a core comprised of certain polymers with additives inclusive of pigment particles therein. Moreover, Japanese Patent Publication abstract No. 53-119044 illustrates an encapsulated toner wherein the marking materials are released by sublimation of the capsule under heat.
With further reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell wherein the shell, such as a polyamide, is formed by an interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions obtained by interfacial polymerization processes, and comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component.
With further reference to the prior art, there is disclosed in U.S. Pat. No. 4,476,211 the preparation of electrostatographic toner materials with surface electroconductivity. Specifically, there is disclosed in the '211 patent a cold pressure fixable toner composition with polyamide, polyurea, and other types of shell materials prepared by an interfacial polymerization process. The colorant selected for these compositions is generally comprised of a variety of dyes or pigments, and the core contains a polymeric material with a binder therein for retaining the colorant within the core and assisting in the fixing of the the colorant onto the surface of a support medium. Examples of high boiling liquids selected for the process of the '211 patent include those boiling at temperatures higher than 180.degree. C. such as phthalic esters, phosphoric acid esters, and alkyl naphthalenes.
Moreover, illustrated in a copending application U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676 relating to cold pressure fixable toners, the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process. Also illustrated in a copending application U.S. Ser. No. 043,265, the disclosure of which is totally incorporated herein by reference, are heat fusible toner compositions comprised of a polymeric core component, and thereover a thermotropic liquid crystalline polymeric shell. By contrast, the toner compositions of the present invention do not contain thermotropic liquid crystalline shells. Low melting characteristics for the compositions of the present invention are rendered possible by the use of multi-component core compositions with components having a sharp melting point as low as 50.degree. C., and by the selection of a lower proportion of shell materials, all other factors being the same.
There thus remains a need for encapsulated toner compositions that possess the improved characteristics illustrated herein. There also is a need for encapsulated toners wherein the shell is ruptured upon heating at low pressures. Further, there is a need for encapsulated toner compositions that will enable images of high optical densities. Also, there is a need for encapsulated toner compositions which can be utilized in electrophotographic imaging apparatuses without release fluid devices. Moreover, there remains a need for low melt toner compositions containing polymers with a softening point between about 50.degree. and 120.degree. C. as the core, and a capsule thereof formulated by interfacial polymerization process. Another need resides in encapsulated low melting toners thereby enabling a significant reduction in the amount of energy required for accomplishing heat fusing of images formulated in electrophotographic apparatuses. There also remains a need for low gloss images after the toner composition is fused to the substrate. Additionally, there is a need for a process allowing the formation of low density toner materials under controlled conditions, and which processes will result in lower cost per copy. There is also a need for encapsulated toners containing both magnetite and carbon black, enabling the control of toner dust in electrophotographic apparatuses. Further, there is also a need for low melt encapsulated toners with acceptable mechanical properties, that is a toner which does not break upon handling in the toner sump or during packaging or storage.